flowevo description of module and communication · 3.3. function of the com signal (communication)...

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smartGAS Mikrosensorik GmbH ▪ Hünderstrasse 1 ▪ 74080 Heilbronn ▪ Phone: +49 (0)7131 / 797553-0

Fax.: +49 (0)7131 / 797553-10 ▪ [email protected] ▪ www.smartgas.eu

FLOWEVO

Description of Module and Communication

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Table of contents

1. General ............................................................................................................. 4

1.1. For your safety ............................................................................................ 4

1.2. Intended use ............................................................................................... 5

1.3. Loss of warranty / liability / disclaimer ............................................................. 5

2. Measurement cell with hose connections ................................................................. 6

2.1. Hose connection / hose material ..................................................................... 6

2.2. Gas flow ..................................................................................................... 7

2.3. Mounting / installation site ............................................................................ 7

3. Assignment and characteristics of the FLOWEVO terminal pins ..................................... 8

3.1. Function of the OUT 1 signal (TTL digital output) ................................................ 9

3.2. The LED status display .................................................................................. 9

3.3. Function of the COM signal (communication) ................................................... 10

4. FLOWEVO register assignment ................................................................................. 11

4.1. Detailed information on the status flags register (Sys_status) ............................. 12

4.2. Detailed information on the unit / scaling of the concentration ............................ 13

5. Communication via Modbus .................................................................................. 14

5.1. Structure of Modbus data telegrams .............................................................. 15

5.2. Structure of UART frames ............................................................................ 16

5.3. Modbus control commands ........................................................................... 17

5.4. Modbus ASCII communication device ............................................................. 21

5.5. Modbus address of the FLOWEVO .................................................................. 22

5.6. Signal profile of the Modbus communication (ASCII operating mode) .................. 24

5.7. Calculating the checksum (ASCII smartGAS operating mode) ............................ 25

6. FLOWEVO zero point and end point calibration .......................................................... 26

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6.1. Zero point calibration .................................................................................. 26

6.2. End point calibration ................................................................................... 28

7. Annex .............................................................................................................. 30

7.1. Mechanical dimensions (mm) ....................................................................... 30

7.2. FLOWEVO operation on a microcontroller .......................................................... 31

7.3. FLOWEVO operation on a PC ......................................................................... 32

8. Service / legal information ................................................................................... 33

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1. General

The FLOWEVO is a refinement of the well known smartMODULFLOW that has been created by

improving on many aspects. Thanks to its convenient interfaces, it is quick and easy to integrate

into existing measuring and control systems.

Below is a list of the major modifications made to the smartMODULFLOW to create the

FLOWEVO:

• Extended operating voltage range of 3.3 V–6.0 V DC (+/- 5%)

• Status display via 2 LEDs (red/green)

• Upgraded software, powerful processor

• Improved mechanical setup, more aesthetic design

• Modbus ASCII (standard and smartGAS-specific) and RTU protocols supported

The FLOWEVO is backward compatible with the smartMODULFLOW; i.e. it can be readily

integrated into existing gas measuring systems.

Based on the physical measurement method of infrared absorption, it provides the best

conditions for reliable and precise measurements, as well as selectivity.

Its compact design and low maintenance effort make it ideal for use in difficult conditions.

1.1. For your safety

• Before connecting and using the FLOWEVO, ensure that you have fully read and

understood these instructions. Please contact our Service department if you have any

questions or if anything is unclear. Important information is written in red. • Store these instructions or pass them on to the device operator for storage, if

necessary; if you sell this device, pass these instructions on to the purchaser. • When installing and operating the device, you must follow the statutory requirements

and guidelines that relate to this product!

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1.2. Intended use

The FLOWEVO is a gas measurement cell with independent measurement capabilities and is

used to determine gas concentrations in accordance with its specifications. It is not suitable for

any other measurement or testing purposes, and must not be used in any other way.

FLOWEVO must not be operated in potentially explosive environments or under harsh conditions

(e.g. high, condensing humidity, heavy air flow, in aggressive atmospheres, or outside without a

housing)!

Please contact our Service department if you have any questions about this.

1.3. Loss of warranty / liability / disclaimer

Opening the sensor, as well as manipulating or damaging the device will invalidate the

warranty!

The warranty may also be invalidated if aggressive chemicals are used, contamination occurs,

liquids penetrate the device or the instructions in this Description of Module and

Communication are not observed!

smartGAS Mikrosensorik GmbH shall not be liable for consequential loss, property damage or

personal injury caused by improper handling or failing to observe the instructions in the

Description of Module and Communication.

Additional information can be obtained from www.smartgas.eu and/or send us at e-mail to

[email protected].

-All rights reserved/subject to change-

Information updated: 06/2017

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2. Measurement cell with hose connections

The housing of the FLOWEVO is made of aluminium to protect the sensor from mechanical

damage. It is equipped with hose connections that ensure that the measurement gas passes

through the measurement process. The actual measurement cell is located between the gas

inlet and the gas outlet – see Figure 1.

Figure 1: FLOWEVO with gas inlet and outlet

2.1. Hose connection / hose material

Hoses must have an inside diameter of 3 mm and an outside diameter of 5 mm to connect to

the measuring cell. Ensure that the hoses are firmly connected to the FLOWEVO.

Please observe the direction of the gas flow, which is indicated by the labels “INLET” and

“OUTLET”. Mixing up the gas flow could result in measurement values that may show

significant deviations from the factory calibration.

Ensure that hoses suitable for measurement are used. Certain applications generate corrosive

gases that could cause problems with the hose material.

INLET OUTLET

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2.2. Gas flow

The gas flow should be constant and between 0.2 l/min and 1.0 l/min. The gas must be dry (dew

point at 5°C) and free from particles.

You can purchase the corresponding filters from smartGAS.

2.3. Mounting / installation site

The smartGAS sensors allow for installation on the customer's devices in various positions.

Since the calibration ex factory cannot cover every installation situation and ambient condition,

the zero point needs to be checked after installation and if necessary recalibrated.

In any case we recommend a functional test of every device after final installation in the

customer's application in the course of commissioning.

Instructions for calibration can be found in chapter 6.

Mount the FLOWEVO using M3 screws with the four M3 threads on the underside of the cuvette;

see Figure 1a for the ideal installation site.

If other installation sites are used, you might need to perform a zero point calibration.

Ensure a minimum clearance of 3 mm to the mounting plate using spacer bolts or spacer

sleeves. You can purchase suitable mounting material from smartGAS.

Do not use the other threads in the device for mounting purposes!

Figure 2: FLOWEVO mounted using spacer bolts

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3. Assignment and characteristics of the FLOWEVO terminal pins

The contact spacing of the connector is 2 mm. The socket is not supplied as standard but can be

ordered separately. (Designation: 4-pin JST connector, 2 mm contact spacing)

Figure 3: Pin assignment of the connector strip on the FLOWEVO

Pins

V+/VC

C

Supply voltage: 3.3 V–6.0 V DC (+/- 5%)

Current draw (max.): 0.3 A

Power consumption (mean value when VCC = 5 V): 600 mW

GND Earth, reference points for all signals / voltages

COM

Communication cable. The sent and received telegrams conform to the Modbus

ASCII or RTU protocol respectively. Individual registers can be read from and

written to via this pin.

OUT 1

TTL digital out. (active = 0) open-collector output. Ensures communication, e.g.

by means of a µ-controller via TTL signals. The individual states are described in

detail elsewhere.

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3.1. Function of the OUT 1 signal (TTL digital output)

The FLOWEVO is capable of displaying its internal device status via the OUT 1 pin (TTL digital

output). The table below shows the coding of the states on the OUT 1 pin.

State Voltage value

Device error L

Everything OK H

The active switching state appears on the open-collector output as a logical 0 or L (LOW).

The OUT 1 connection is designed as an open-collector connection. It switches to GND and

may be loaded with a maximum of 30 mA. The voltage must never exceed 30 V DC. An anti-

surge diode must be used when inductive loads are being switched!

3.2. The LED status display

Two LEDs (green/red) are located next to the connector stip. These show the current device

status as per the table below:

Green

LED

Red LED Device status

Off off No operating voltage / device switched off

Flashing off Start phase / self-test (approx. 40 seconds)

On off Normal operation

Off On System error � Contact Service!

Figure 4: Position of the status LEDs

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3.3. Function of the COM signal (communication)

The FLOWEVO has a half-duplex UART data interface that supplies and evaluates the non-

inverted UART signals. The half-duplex operation also means that only one communication

signal (COM) is required. The level on the COM cable is between 0 V and +3.3 V. It may

therefore be necessary to include a voltage level translation depending on the communication

partner (master) connected.

The COM connection is designed as an open-collector connection with an internal pull-up of 10

kOhm to 3.3 V. It is wired to GND and may be loaded with a maximum of 30 mA. The voltage

must never exceed 7 V DC. The use of protective resistors, EMC filters, electrical isolation and

other electrical or electronic measures may cause communication problems and must therefore

be carefully considered by specialist personnel.

The protocol used at user level is Modbus ASCII (original or smartGAS-specific) or RTU.

FLOWEVO automatically adjusts itself to the communication method. This affects both the baud

rate and the framing. The Modbus dialect used is also detected automatically. FLOWEVO

essentially acts as a slave, which means that it waits for being contacted from a master.

For the automatic communication detection to function reliably, some conditions must be

observed:

• Communication no earlier than 100 ms after switching on the FLOWEVO.

• To detect communication, the master must send the first data telegram without gaps

in the byte string.

• No change in baud rate, framing or Modbus dialect during operation. If a change is

necessary, you must switch the operating voltage of the FLOWEVO off and on again.

• Supported baud rates: 2400, 4800, 9600, 19200 (Modbus standard), 38400, 57600 and

115200.

• Supported framing in Modbus ASCII (original or smartGAS-specific): 7E1 (Modbus

standard), 7E2, 7O1, 7O2, 7N2, 8E1, 8O1, 8N1 and 8N2.

• Supported framing in Modbus RTU: 8E1 (Modbus standard), 8O1, 8N1 and 8N2.

Chapter 5 provides a detailed overview of the communication.

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4. FLOWEVO register assignment

The FLOWEVO registers available to the user are shown in the following table. All registers can

be read but only some are writeable, as the table shows:

Reg.

address

Register

name

Write Data

type

Function/explanations

0x0003 T_m No Signed

number

Internal sensor temperature as reference

point for the temperature error correction in

multiples of 0.1°C.

0x0009 Sys_status No Number System status as a bit string. The meaning of

the individual bits is explained later in this

document.

0x000A Conc No Signed

number

Measured concentration value. The

concentration unit and the scaling are

produced together with the unit code.

Calculation example later in this document.

0x0047 IR_4tagneu Yes Number Zero point reference value.

0x004F Unit No Number Unit code and scaling factor for the

concentration. Details and calculation

example later in this document.

0x0054 Span Yes Number End point reference value.

0x0080-

0x0083

DeviceType No String Indicates the type of the connected device

0x0084-

0x0085

SW version No String Software version of the connected device

0x0086-

0x0089

Serial No No String Serial number of the connected device

0x00C0 Modbus_ad

dress

Yes Number Modbus address of the FLOWEVO. Once this

address has been changed, communication

with the FLOWEVO can continue only via the

new address.

The device also has additional registers that are used for diagnostic, setting and calibration

purposes. Write access to registers that are not listed in the table cause the device to function

incorrectly and is therefore forbidden!

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4.1. Detailed information on the status flags register (Sys_status)

Status flags register (Sys_status 0x0009)

15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

Re

serv

ed

Po

we

r_O

n

WD

G_W

arn

EE

P_E

rro

r

MW

_act

ive

To

x

Ex

Inc

MW

_ok

Co

rr

Sta

rtu

p

Wa

rn

Ala

rm

Sys

err

Wa

rmu

p

Te

st

The meaning of the individual status flags, from right to left, is:

Flag 0: Test flag, Value “1” when the self-test has been triggered

Flag 1: Warmup, Value “1” during warm-up phase after start (appr. 10 sec)

Flag 2: Syserr, Value “1” in case of a device and/or system error

Flag 3: Alarm, Value “1” in case of gas primary alarm

Flag 4: Warn, Value “1” at the gas pre-alarm

Flag 5: Startup, Value “1” in the start-up phase (approx. 40 sec)

Flag 6: Corr, Value “1” when the correction function is active (always)

Flag 7: MW_ok, Value “1” when the zero point has been set

Flag 8: Inc, Value “1” when inc concentration has been reached

Flag 9: Ex, Value “1” when ex concentration has been reached

Flag 10: Tox Value “1” when Tox concentration has been reached

Flag 11: MW_active, Value “1” when averaging for drift correction is active

Flag 12: EEP_error, Value “1” when EEprom error

Flag 13: WDG_Warn, Value “1” when watchdog has responded

Flag 14: Power_On, Value “1” when voltage has been switched on

Flag 15: Reserved Always 0

The two flags 6 (Corr) and 7 (MW_ok) are internal flags set in the manufacturing process of the

individual FLOWEVO. They are also used for quality control purposes and are set at the value “1”

if the respective FLOWEVO has been temperature-compensated and calibrated.

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4.2. Detailed information on the unit / scaling of the concentration

The Conc register (0x000A) provides a numeric value that varies in terms of its scaling and unit

depending on the design FLOWEVO. The Unit register (0x004F) can be used to correctly calculate

the concentration value. The meaning of the numeric value in the Unit register (0x004F) is

therefore displayed as follows:

Value = 0: Unassigned Reserved for special applications

Value = 1: ppm x 0.01 or ppb x 10

Value = 2: ppm x 0.1 or ppb x 100

Value = 3: ppm x 1 or ppb x 1000

Value = 4: Vol% x 0.001 or ppm x 10



Value = 7: %UEG x 0.01 Lower explosion limit

Value = 8: %UEG x 0.1 Lower explosion limit

ppm stands for 1 x 10-6 volume fraction of the measurement gas in terms of the total gas

volume. ppb stands for 1 x 10-9 volume fraction of the measurement gas in terms of the total gas

volume. Vol% stands for 1 x 10-2 volume fraction of the measurement gas in terms of the total

gas volume. UEG indicates the measurement gas content in the air necessary for there to be an

explosive mixture.

Example 1:

If the value in the Conc register (0x000A) is 3425 and the value in the Unit register (0x004F) is 2,

the correctly scaled concentration provided with the unit is 3425 x (ppm x 0.1) = 342.5 ppm.

Example 2:

If the value in the Conc register (0x000A) is 7236 and the value in the Unit register (0x004F) is 5,

the concentration is 7236 x (Vol% x 0.01) = 72.36 Vol%.

The scaling factor and the concentration unit can also be found on the QA accompanying

certificate enclosed with every FLOWEVO.

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5. Communication via Modbus

The FLOWEVO supports the Modbus protocol in ASCII and RTU mode thanks to its serial half-

duplex interface. In ASCII mode, in addition to the standard variant, there is a smartGAS-

specific derivative that differs from the standard in terms of the checksum calculation.

Modbus communication is fundamentally based on a query/response mechanism. A master

sends the query to one of perhaps multiple slaves (subscribers). Each connected subscriber

therefore has a subscriber address that is unique in the network. Only the subscriber that has

found its address in the query from the master will respond.

The type of query is determined by a control command (function code). This can, for example,

be about writing data or reading data to/from the subscriber. Depending on the control

command, there is a data portion for both the query and the response.

Each query and each response must be clearly identified by its beginning and by its end. It will

also be helpful to add a test field to the transported data again so that potential communication

errors can be detected. The Modbus derivatives implement this in different ways.

You can obtain detailed information about the Modbus protocol at www.modbus.org

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5.1. Structure of Modbus data telegrams

The following two tables show the basic structure of an ASCII data telegram and a RTU data

telegram. The tables show that the address, control command and data portion are based on

the same source data for both telegram types:

Dialect Start Address Control Data LRC End

Modbus

ASCII

1

character

‘:’

2

characters,

e.g.: “A0”

2

characters,

e.g.: “03”

0 to 2x252 characters,

e.g.: “00050002”

2

characters,

e.g.: “A6”

2

character

s CR, LF Communi

cation: 0x3A 0x41, 0x30 0x30, 0x33

0x30, 0x30, 0x30,

0x35, 0x30, 0x30,

0x30, 0x32

0x41, 0x36 0x0D,

0x0A

Dialect Start Address Control Data CRC End

Modbus

RTU 1 byte, e.g.:

0xA0

1 byte, e.g.:

0x03

0 to 1x252 bytes, e.g.:

0x00, 0x05, 0x00,

0x02

2 bytes,

e.g.:0xA4,

0xD3

Communi

cation:

Pause,

3.5 char 0xA0 0x03

0x00, 0x05, 0x00,

0x02 0xA4, 0xD3

Pause,

3.5 char

In ASCII mode, each 8-bit byte is therefore sent as two ASCII characters. One byte can also be

seen as two nibbles. One nibble has 4 bits and represents precisely one hexadecimal number.

As can be seen in the telegram examples, the result of the byte containing the information

“0xA6” is the two ASCII characters “0x41” = ‘A’ and “0x36” = ‘6’.

In ASCII mode, 7 data bits are sufficient for transporting the characters via the interface. The

ASCII mode has a historical advantage. All Modbus data telegrams can be “read” with an ASCII

terminal; plain text appears on the screen.

In RTU mode, however, each 8-bit byte is handed over unchanged. This inevitably means that

in RTU mode UART frames with 8 data bits need to be used. The advantage of the RTU mode

lies in the more effective utilisation of the interface because only around half of the data

volume needs to be transmitted compared to the ASCII mode.

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5.2. Structure of UART frames

A UART frame is structured as follows:

Start N data bits Parity M stop

1 start bit (always 0), followed by

7 or 8 data bits, starting with the lowest-value bit,

1 parity bit (optional). If used, the parity bit can be even or odd,

1 or 2 stop bits (always 1).

The nomenclature for describing a UART frame consists of a number, followed by a letter and

ending with a number. The first number says how many data bits the frame contains. The

following letter describes the type of parity with N for none, E for even and O for odd. The last

number indicates how many stop bits are being sent. The standard specification for Modbus

RTU is 8E1, and 7E1 for Modbus ASCII.

Examples:

8N1 means that 8 data bits are being used, there is no parity (N) and 1 stop bit is being used.

7E1 means that 7 data bits are being used, there is even parity (E) and 1 stop bit is being used.

Furthermore, when transporting a UART frame via the electrical cable, how “quickly” the

transmission occurs is important. The term baud rate is a definition for this. The baud rate

describes how many bits are transmitted per second. Standard baud rates are 2400, 4800,

9600, 19200 (Modbus standard), 38400, 57600 and 115200. All of these are fully supported by

FLOWEVO.

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5.3. Modbus control commands

Two command codes (function codes) are sufficient for communication with FLOWEVO. These

are 0x03 – Read (multiple) holding registers and 0x06 – Write (exactly one) register. One

register is 16 bits wide and therefore consists of 2 bytes:

Register 15 … 0

High order byte – Hi Low order byte – Lo

All the FLOWEVO data that the user can access is shown on registers that are each 16 bits wide.

The two control commands will now be explained using some examples.

Control command 0x03 – Read (multiple) holding registers

This control command allows you to read values from the FLOWEVO. The main thing is that only

defined registers can be read. This must therefore be checked especially when queries are sent

to multiple registers. Chapter 4 has information on register assignment.

Example 1 – Reading out the 4 registers for “Device Type”:

Request Reply Meaning of the data

Field (Hex) Field (Hex)

Control command 03 Control command 03

Hi start address 00 Number of bytes 08

Lo start address 80 Hi register value 53 ‘S’

Number of Hi 00 Lo register value 4D ‘M’

Number of Lo 04 Hi register value 46 ‘F’

Lo register value 43 ‘C’

Hi register value 4F ‘O’

Lo register value 32 ‘2’

Hi register value (131) 20 ‘ ’ = Empty

Lo register value (131) 20 ‘ ’ = Empty

In this example, 4 registers of the FLOWEVO were read starting from register start address

0x0080 (decimal 128). The response consisted of a payload of 8 bytes. This was clearly a CO2

module. The 3 letters SMF mean that it is a FLOW sensor.

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Example 2 – Reading out the “Conc” register:





Lo start address 0A Hi register value (10) 01 Concentration is 456

Number of Hi registers 00 Lo register value (10) C8

Number of Lo registers 01

In this example, exactly one register was read starting from register start address 0x000A

(decimal 10). The two data bytes were transmitted combined as a hexadecimal value. If this

value is converted to a decimal number, the result is a concentration of 456.

Example 3 – Reading out the “Unit” register:





Lo start address 4F Hi register value (79) 00 3, means ppm x 1

Number of Hi registers 00 Lo register value (79) 03

Number of Lo registers 01

In this example, exactly one register was read starting from register start address 0x004F

(decimal 79). The two data bytes were transmitted combined as a hexadecimal value. If this

value is converted into a decimal number, the result is 3. This stands for the unit ppm with the

scaling x 1. Combined with the data from examples 1 and 2, the FLOWEVO that was read has

therefore measured a gas concentration of 456 ppm CO2.

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Control command 0x06 – Write to (exactly one) register

This command enables a new value to be written to a certain register. However, registers are

only writeable if they are intended for it. For more information on this, see register assignment

in Chapter 4.

Example 1 – Writing to the “Modbus_address” register:




Hi register address 00 Hi register address 00

Lo register address C0 Lo register address C0

Hi register value 00 Hi register value (192) 00 The new address of

the module (160) Lo register value A0 Lo register value (192) A0

In this example, a new Modbus address for the FLOWEVO was set. Once this communication

sequence is complete, the device is only responsive at the new address!

Example 2 – Writing to the “IR_4tagneu” register:





Lo register address 47 Lo register address 47

Hi register value (71) 00 Hi register value (71) 00 The zero point has

been reset (1) Lo register value (71) 01 Lo register value (71) 01

In this example, the zero point FLOWEVO has been reset. This occurred by writing the value 1 to

register 0x0047 (decimal 71). The device has subsequently internally calculated and saved the

current corrected value for the zero point. Reading out the same register then shows the fixed

value of the correction.

The zero point must only be set when zero gas and then a stable concentration value are

applied! You can find more information in Chapter 6.

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Example 3 – Writing to the “Span” register:





Lo register address 54 Lo register address 54

Hi register value (84) 27 Hi register value (84) 27 Span was set to

10000 (pre-Lo register value 10 Lo register value (84) 10

In this example, a new end point correction for the FLOWEVO was set. A value of 10000 means

that the correction factor is 1.0000. This is also the delivery condition. A value of 11000 would

mean that the concentration value displayed is 10% higher than internally measured. This

register therefore enables deviations of the FLOWEVO in the concentration display to be

corrected. It stands to reason that the current Span value is read first so that it is clear how the

new value can be calculated.

The end point must only be set in this way when a suitable test gas and then a stable

concentration value are applied! More information is available in Chapter 6.

Setting the end point only makes sense if the zero point has previously been set correctly.

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5.4. Modbus ASCII communication device

Figure 5 shows the state diagram of the transmission and receiving devices in principle,

regardless of whether it is master or slave.

Figure 5: State diagram of a Modbus subscriber (ASCII operating mode)

If an incomplete query is sent to the FLOWEVO it does not return a response. The module

behaves the same if at least one register in the register area being queried does not exist. Error-

free telegrams are processed, others are discarded.

Waiting (ready to

send or receive)

Start

sending

Receive

Send

Sending

end

Wait for end of

telegram

Request

Receive ‘:’ (0x3A)

Receive characters/

set characters in the

receive buffer

Receive ‘:’ (0x3A) /

empty receive buffer

Receive CR

(0x0D)

Receive ‘LF’ (0x0A) / check

received telegram (LRC,

parity, slave address, etc.)

Sending ‘:’ (0x3A)

Sending ‘CR’, ‘LF’

(0x0D, 0x0A)

Send all

characters

Receive ‘:’ (0x3A)/

empty receive buffer

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5.5. Modbus address of the FLOWEVO

In the examples above, the focus has been on the control commands without mentioning the

scope of the telegram in detail. However, the telegram also includes the address of the slave

subscriber, which is either queried or delivers a response to a query.

With the FLOWEVO, the device address as delivered corresponds to the last two digits of the

serial number of the FLOWEVO – see Figure 6.

Figure 6: Determining the Modbus address of the FLOWEVO as delivered

Figure 7 is a flow diagram that shows how unknown Modbus module addresses can be

determined. Now, any register (e.g. serial number) can be queried via all module addresses (1–

247) with a timeout of one second. If a module is queried with the correct address, it reacts by

sending a response. The module address is included in this response. Thus, at the end of the

search cycle, module responses can be used to check which module addresses are presently

connected to the bus system. When querying the serial numbers, it is even possible to conclude

which address is assigned to which module.

The permitted address range for the FLOWEVO is between 1 and 247. According to Modbus

specifications, the addresses 248–255 are reserved. Address 0 stands for broadcast.

Please note:

Device address = #35 Decimal � 0x23 Hex If

the serial number ends with “00”, the

address is always #100 decimal = 64

hexadecimal.

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Figure 7: Flow diagram – determining unknown addresses of the modules being used (Modbus

ASCII operating mode)

Connect module

Query telegram for reading out the serial number

: Addr. 03 0086 0004 LRC CRLF

Timeout: = 1s

Addr.: = 1 to 247 STEP 1

Calculate LRC

Timeout

Output serial

no. and

address

Send query

Valid

response

Addr. = 48?

START

STOP

Y

No

No

No

Y

Y

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5.6. Signal profile of the Modbus communication (ASCII operating

mode)

Figure 8 shows a potential scenario of a data exchange between the master and the connected

subscriber/s (primarily FLOWEVO). This assumes a baud rate of 2400 and the Modbus

communication running in ASCII mode. Times vary accordingly for other baud rates.

Figure 8: Time diagram – data exchange between master and BASICEVO

The duration of a query string is 70–73 ms. A brief pause (max. 400 ms) may then follow. The

module response then follows. This depends on the number of bytes being read out. If only one

byte is read out, the module response is approx. 70 ms. When multiple bytes are being read

out, the response phase is correspondingly longer.

Basically, it can be said that the FLOWEVO reacts to a correct query reliably within 400 ms. The

character string is then sent immediately without a response pause.

Data

Gas module

Databus

Data exchange n-1 Reading one byte

Data exchange n Reading multiple bytes

Request Idle time Request Idle time

Analysis of the response and preparation of the next query

Analysis of the response and preparation of the next query

Processing the query

Response

Processing the query

Response

The response time depends on

the number of data bytes

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5.7. Calculating the checksum (ASCII smartGAS operating mode)

This subchapter explains the calculation of the checksum (LRC) specifically for the ASCII

smartGAS operating mode. How the calculation of the LRC checksum in ASCII standard and

CRC checksum in RTU functions is described thoroughly in the documents of the Modbus

standard. It is helpful to have a conversion table for ASCII values in hexadecimal and decimal

format as follows:

ASCII ‘0’ ‘1’ ‘2’ ‘3’ ‘4’ ‘5’ ‘6’ ‘7’ ‘8’ ‘9’ ‘A’ ‘B’ ‘C’ ‘D’ ‘E’ ‘F’

Hex 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46

Dec. 48 49 50 51 52 53 54 55 56 57 65 66 67 68 69 70

The checksum is calculated using the address, the control command and the associated data

after the conversion to ASCII has occurred. By way of example, we generate a query for reading

out the Conc register from the FLOWEVO with the address 35 (decimal).

Therefore, in hexadecimal format, the resulting byte string is 0x23, 0x03, 0x00, 0x0A, 0x00,

0x01. After the ASCII conversion, the result is the data string 2303000A0001. The data string is

now converted and the checksum is formed:

Address Command Start register Number of registers Sum

ASCII 2 3 0 3 0 0 0 A 0 0 0 1 ---

↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓

Dec. 50 51 48 51 48 48 48 65 48 48 48 49 602

Sum = 602

Checksum = 255 – 602 + 1 = - 346

Modulo sum(256) = - 346 + 256 + 256 = 166 (dez.) → A6 (ASCII hex.)

Putting the starting character at the beginning and the calculated checksum and end code at

the end would mean that the following data string would be sent:

:2303000A0001A6<CR><LF>

The checksum is included each time data is sent and is then recalculated by the recipient again.

If the data set is corrupted or changed, the checksum calculated by the recipient would deviate

from that which was sent. The data set would then be unusable.

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6. FLOWEVO zero point and end point calibration

The following explanations concern the calibration of the FLOWEVO via Modbus (ASCII operating

mode in the smartGAS variant). Examples are used to describe the communication content for

exactly this operating mode. A requirement here is that a corresponding communication partner

is available, ready for operation and connected. The examples refer to a FLOWEVO module with

the Modbus address 35 (0x23); the checksums are shown as symbols and can be determined

using the information Chapter 5.7.

The FLOWEVO must be in operation for 30 minutes before calibration can be carried out! The

calibration gas concentration (zero and end point) must be stable. This may take a few minutes

depending on the boundary conditions! Unless otherwise specified for the application, we

recommend testing the sensors at least every 12 months.

6.1. Zero point calibration

To calibrate the zero point, zero gas must be flowing in the FLOWEVO. Furthermore, you must

ensure that the measured concentration value is sufficiently stable. This occurs by reading out

the Conc register (0x00A) again. If the value only fluctuates by a few digits, the zero point can

be set.

Reading out the Conc register:

Sending the following command to the FLOWEVO (checksum in symbols):

“:2303000A0001XX<CR><LF>”

Start Address 35 Read Start register 0x000A Number of registers: 1 Checksum

: 23 03 00 0A 00 01 XX

The following response is sent (the file contents may deviate, checksum in symbols):

“:230302001AYY<CR><LF>”

Start Address 35 Read Number of bytes: 2 Data: 26 Checksum

: 23 03 02 00 1A YY

The content of the Conc register is 26, which indicates that it makes sense to set the zero point.

If this value remains stable over a longer time period, the zero point can be set.

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Setting the zero point by writing to the IR_4tagneu register:

To do this, the value 1 must be written to the “IR_4tagneu” register (0x0047). For FLOWEVO, the

value 1 is the indicator to value the measured concentration as exactly 0.

We strongly recommend not writing any other value than 1 to the register because this could

shift the zero point significantly!


“:230600470001ZZ<CR><LF>”

Start Address 35 Write Register: 0x0047 Data: 1 Checksum

: 23 06 00 47 00 01 ZZ

If the command was correctly transmitted, the same command is sent back as a response.

It can now be verified that the concentration value is quite close to 0 by querying to Conc

register (0x000A) as previously described above.

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6.2. End point calibration

Setting the end point requires that FLOWEVO has an exact zero point as a reference.

We strongly recommend carrying out a zero point calibration as described above before

calibrating the end point.

The concentration of the test gas used for the end point calibration should be between 50% and

100% of the FLOWEVO measuring range. Lower concentration test gases could lead to a

significant loss of accuracy. Higher concentration test gases could not be measured exactly.

The end point is determined in the FLOWEVO via the “Span” register (0x0054). This register

contains a correction value (presetting 10000) that is used to evaluate the internally measured

concentration. The concentration scaled using this is available in the previously explained Conc

register (0x000A).

For the end point calibration to be successful, the “Span” register (0x0054) must be read out

first as a value that does not equal 10000 could already be present.

Reading out the Span register:


“:230300540001XX<CR><LF>”

Start Address 35 Read Start register 0x0054 Number of registers: 1 Checksum

: 23 03 00 54 00 01 XX

The following response is sent (the file contents may deviate, checksum in symbols):

“:2303022701YY<CR><LF>”


: 23 03 02 27 01 YY

FLOWEVO therefore contains 9985 as the value in Span. This value must be noted; we call it

Span_OLD.

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To calibrate the end point, test gas of a known concentration must be flowing in the FLOWEVO.

Furthermore, you must ensure that the measured concentration value is sufficiently stable. This

occurs by reading out the Conc register (0x00A) again as described for the zero point calibration.

If the value only fluctuates by a few digits, it can be used.

Reading out the Conc register:


“:2303000A0001XX<CR><LF>”

Start Address 35 Read Start register 0x000A Number of registers: 1 Checksum

: 23 03 00 0A 00 01 XX

The following response is sent (the file contents can deviate, checksum in symbols):

“:23030203D2YY<CR><LF>”


: 23 03 02 03 D2 YY

The sensor therefore indicates a Conc_OLD concentration of 978. The concentration of the

Conc_CAL test gas is 1003, for example.

Recalculating the value for Span:

Span_NEW = Conc_CAL * Span_OLD / Conc_OLD = 1003 * 9985 / 978 = 10240

Setting the end point by writing to the Span register:

To do this, the value 10240 that was just calculated must be written to the “Span” register

(0x0054).


“:230600542800WW<CR><LF>”

Start Address 35 Write Register: 0x0054 Data: 10240 Checksum

: 23 06 00 54 28 00 WW

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If the command was correctly transmitted, the same command is sent back as a response.

It can be verified that the concentration value is quite close to the test gas value of 1003 by

querying the “Conc” register (0x000A) as previously described above.

7. Annex

7.1. Mechanical dimensions (mm)

Cuvette length A B C

45 mm 30 30 73

85 mm 70 70 113

105 mm 90 90 133

125 mm 110 110 153

205 mm 190 190 233

245 mm 230 230 273

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7.2. FLOWEVO operation on a microcontroller

For the FLOWEVO to communicate with a microcontroller, the level of the signals at the module

COM pin must be adapted to the microcontroller. The easiest way to do so is using an RS485

interface module that must be selected according to the microcontroller voltage supply.

The TXD (transmit data), RXD (receive data) and a signal for activating the TXEN (transmitter

enable) UART signals must be provided at the microcontroller. The following figure shows the

circuit:

Figure 9: FLOWEVO on a microcontroller

The circuit is designed for a microcontroller with 5 V operating voltage. When operating at 3.3

V, use a ADM3075 (or equivalent types) rather than the ADM4850 (or equivalent types). All

other components are unaffected.

Up to 16 FLOWEVO can be operated in parallel with this circuit. This requires the devices to have

different Modbus addresses.

It should be noted that FLOWEVO must be connected to a power supply in addition to the

communication connection shown above.

Microcontroller

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7.3. FLOWEVO operation on a PC

Operating exactly one FLOWEVO on a PC requires a suitable USB adapter incl. software; this

can be purchased from smartGAS as an accessory. The FLOWEVO is powered via the USB port;

an additional power supply is not necessary. The following figure shows such an adapter:

Figure 10: USB adapter for operating the FLOWEVO on the PC

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8. Service / legal information

Our Service department is your partner at all times. We guarantee you full

satisfaction, expert advice and top quality.

Service and support:

Please contact your distributor or us directly at:

Tel.: +049 7131 / 797553-0 or by e-mail [email protected]

You can also contact us via our website www.smartgas.eu.

Legal information:

smartGAS FLOWEVO Description of Module and Communication

© smartGAS Mikrosensorik GmbH

Edition V1.42 / June 2017

The figures and drawings used in this description may differ from the originals;

the solely serve illustrative purposes.

All information – including technical specifications – is subject to change without notice.

smartGAS Mikrosensorik GmbH

Hünderstrasse 1

74080 Heilbronn

Germany

Telephone +49 7131 797553-0

Fax +49 7131 797553-10

www.smartGAS.eu

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